1. Field of the Invention
The present invention relates to an organic light emitting display having a DC-DC converter.
2. Description of the Related Art
DC-DC converters are generally used to convert a direct current (DC) voltage of a power supplier to have an appropriate voltage for electronic equipment such as a mobile phone, a personal digital assistant (PDA), a portable multimedia player (PMP), an MP3 player, a digital camera, or a camcorder.
When an organic light emitting display is used as a display for the electronic equipment, the DC-DC converter should concurrently supply a positive power voltage and a negative power voltage to the organic light emitting display.
To this end, the DC-DC converter may include a boost converter that outputs a positive power voltage and an inverter that outputs a negative power voltage. Both the boost converter and the inverter may include an inductor, a switch, a freewheel diode, and a capacitor. And, the DC-DC converter may include a switching controller for controlling each switch of the boost converter and the inverter. As described above, the DC-DC converter that outputs two output voltages is generally called a dual output converter. Further, the switching controller may be integrated into one semiconductor chip.
As described above, the DC-DC converter including the boost converter and the inverter generally has two freewheel diodes for circulating energy. Each freewheel diode is electrically coupled outside the switching controller, which is integrated in one semiconductor chip, and causes a voltage drop of approximately 0.4 to 0.7V. Therefore, there is a problem in that the power consumption is high and the overall size and the weight of the DC-DC converter is increased.
Further, since the above-described freewheel diodes are coupled in the power supply direction, that is, the forward direction, the power of the power supply may be continuously supplied to the organic light emitting display even when the switching controller does not operate. In other words, the conventional DC-DC converter cannot be truly shut down due to the freewheel diode. Therefore, the power of the power supplier is continuously supplied to the organic light emitting display even when the DC-DC converter or the switching controller does not operate. Accordingly, there are problems in that the power of the power supplier is consumed and the organic light emitting display deteriorates.